1. Field of the Invention
The present invention generally relates to a field effect transistor and to a method for forming the field effect transistor, and more particularly, the present invention relates to MISFET(Meta-Isulator Semiconductor Field Effect Transistor) and MOSFET (Metal-Oxide Semiconductor Field Effect Transistor) and to methods for forming the same.
This application is a counterpart of Japanese application Ser. No. 229533/1997, filed Aug. 26, 1997, the subject matter of which is incorporated herein by reference.
2. Description of the Related Art
In general, a conventional field effect transistor has disclosed "(1) Hot carrier kouka (effect), Etsuji Takeda, Nikkei Mc Graw Hill, pp. 63-71, and (2) Mater. Res. Proc. 105, K. Taniguchi et al., 1988, pp. 139-144". While the MOS FET achieves high device integration, the hot-carrier effect, for example, makes it difficult to secure needed reliability.
FIG. 1 is a sectional view for describing a hot carrier effect mechanism of the conventional MOSFET.
As shown in FIG. 1, the conventional MOS FET is made up of a silicon substrate 21, a heavily doped drain 22, a heavily doped source 23, a lightly doped drain 24, a gate oxide film 25, a gate electrode 26, and a side wall oxide film 27. The hot-carrier induced damage in the MOS FET has been found to result in either trapping of carriers at defective sites in the oxide or the creation of interface states at the silicon-oxide interface, or both. The damage caused by hot-carrier injection affects the transistor characteristics by causing a degradation in trans conductance, a shift in the threshold voltage, and a general decrease in the drain current capability. The LDD (Lightly Doped Drain)-MOS FET structure has been used to minimize this hot carrier effect problem.